1. Field of the Invention
The invention relates to an engine generator, and more particularly, to an engine generator which uses a generator driven by an engine as an engine starting electric motor.
2. Description of the Related Art
An engine generator has diffused into widespread practice as a power supply device for various kinds of uses such as portable use and emergency one. In recent years, an engine generator has been also used as an engine starting electric motor, especially, responding to a demand for smaller size and reduction in the number of components.
If the alternating current (AC) output of the engine generator is, for example, 100 V AC when an engine generator is also used as an engine starting electric motor, a direct current power supply (high voltage battery) of about 140 V is required to drive the generator as an engine starting electric motor, because an output of 140 V or more is required as a peak value of the generator itself.
Moreover, generally, a generator output circuit and an electric motor starting circuit are separately provided and those circuits are used by switching for operation as a generator and as an electric motor in order to operate the generator as an electric motor when an engine is started and as a generator after the engine is started.
An engine generator, in which a generator output circuit is also used as an electric motor starting circuit, has been proposed. For example, an engine generator has been proposed in the Japanese Patent Application Laid-open No. H5-292799. According to the engine generator comprising an AC generator connected to an engine, a power conversion equipment with an electronic power rectifier and an electronic power inverter, and a battery for engine starting, wherein inverter operation of the electronic power rectifier is executed, using the battery as a power supply, when the engine is started, and an electric motor operation of the AC generator is performed, the cost for the electronic power rectifier is reduced by the rectifier comprising a half bridge circuit.
However, in a previous engine generator, a high voltage battery with a capacity of more than the output of the generator is required as described above in order to drive the generator as an engine starting electric motor. But the high-voltage battery is expensive. Moreover, the engine generator in which a generator output circuit and an electric motor starting circuit are separately provided has not met the demand for smaller size and reduction in the number of components.
Though the number of components can be reduced in the previous engine generator, in which the generator output circuit is also used as the electric motor starting circuit as proposed in the above-described publication, there has been a problem that separate switching of wiring connection for operation as an electric motor (when an engine is started) and as a generator is required to make the configuration and the control complex, because a part of an inverter for obtaining AC output, or a reactor on its output side is used as a converter for step up of voltage.